Epigenetic alterations play an important role in the regulation of cellular processes, including cell proliferation, cell differentiation and cell survival. The epigenetic silencing of tumor suppressor genes and activation of oncogenes may occur through alteration of CpG island methylation patterns, histone modification, and dysregulation of DNA binding protein. Polycomb genes are a set of epigenetic effectors. EZH2 (enhancer of zeste homolog 2) is the catalytic component of the Polycomb Repressor Complex 2 (PRC2), a conserved multi-subunit complex that represses gene transcription by methylating lysine 27 on Histone H3 (H3K27). EZH2 μlans a key role in regulating gene expression patterns that regulate cell fate decisions, such as differentiation and self-renewal. EZH2 is overexpressed in certain cancer cells, where it has been linked to cell proliferation, cell invasion, chemoresistance and metastasis.
High EZH2 expression has been correlated with poor prognosis, high grade, and high stage in several cancer types, including breast, colorectal, endometrial, gastric, liver, kidney, lung, melanoma, ovarian, pancreatic, prostate, and bladder cancers. See Crea et al., Crit. Rev. Oncol. Hematol. 2012, 83:184-193, and references cited therein; see also Kleer et al., Proc. Natl. Acad. Sci. USA 2003, 100:11606-11; Mimori et al., Eur. J. Surg. Oncol. 2005, 31:376-80; Bachmann et al., J. Clin. Oncol. 2006, 24:268-273; Matsukawa et al., Cancer Sci. 2006, 97:484-491; Sasaki et al. Lab. Invest. 2008, 88:873-882; Sudo et al., Br. J. Cancer 2005, 92(9):1754-1758; Breuer et al., Neoplasia 2004, 6:736-43; Lu et al., Cancer Res. 2007, 67:1757-1768; Ougolkov et al., Clin. Cancer Res. 2008, 14:6790-6796; Varambally et al., Nature 2002, 419:624-629; Wagener et al., Int. J. Cancer 2008, 123:1545-1550; and Weikert et al., Int. J. Mol. Med. 2005, 16:349-353.
Recurring somatic mutations in EZH2 have been identified in diffuse large B-cell lymphoma (DLBCL) and follicular lymphomas (FL). Mutations altering EZH2 tyrosine 641 (e.g., Y641C, Y641F, Y641N, Y641S, and Y641H) were reportedly observed in up to 22% of germinal center B-cell DLBCL and 7% of FL. Morin et al. Nat. Genetics 2010 February; 42(2):181-185. Mutations of alanine 677 (A677) and alanine 687 (A687) have also been reported. McCAbe et al., Proc. Natl. Acad. Sci. USA 2012, 109:2989-2994; Majer et al. FEBS Letters 2012, 586:3448-3451. EZH2 activating mutations have been suggested to alter substrate specificity resulting in elevated levels of trimethylated H3K27 (H3K27me3).
Accordingly, compounds that inhibit the activity of wild type and/or mutant forms of EZH2 are of interest for the treatment of cancer.